1. Field of the Invention
The present invention relates to a signal conditioning apparatus and method for determination of permanent magnet motor rotor position.
2. Related Art
Rotor position information is in general required for stable operation of permanent magnet AC motors. Continuous rotor position can be obtained from an encoder mounted on a motor shaft or obtained indirectly through estimation algorithms (based on voltage and current feedbacks). The latter is preferred for lower system and operating cost.
Back EMF-based sensorless control methods cannot sustain low and zero speed operations. Applications such as electric vehicles, power steering, electric scooter and traction systems all require full torque control down to zero speed. Signal injection techniques have been suggested to enable continuous low speed operation of a permanent magnet motor. By injection of high frequency (typically 0.5 to 2 KHz) current into the motor, the rotor position can be extracted from the negative sequence component of the injected high frequency current. The negative sequence component contains information on the rotor magnetic axis. However, the magnetic axis polarity (North or South) information is not present in the negative sequence component. Therefore, the magnetic axis polarity has to be computed by extra means before drive torque application.
Signal injection methods have been proposed which utilize complex synchronously rotating frame filters to extract rotor magnetic axis information from the negative sequence current component. It would be desirable to provide a simplified technique to extract rotor position information from a negative sequence current component.